Complex inorganic colored pigments are based upon crystalline mixed-metal oxide materials. This class of materials is well-known in the art and is described, for example, in High Performance Pigments by Hugh MacDonald Smith, Wiley-VCH, 2002, and the published brochure, Classification and Chemical Description of the Complex Inorganic Color Pigments, 3rd Ed., 1991, Colored Pigment Manufacturer's Association (formerly the Dry Color Manufacturer's Association), both incorporated herein by reference. Another reference which describes CICPs is the Pigment Handbook, Vol. 1 Properties and Economics, 2nd Ed., Peter A. Lewis (ed.), John Wiley & Sons, 1988 (see particularly chapters C.e.2, C.e,3, C.e.6, and C.e.7), incorporated herein by reference.
The use of the term “Complex Inorganic Color Pigments” is a relatively recent one. These pigments have been referred to as ceramic pigments, synthetic inorganic complexes and mixed metal oxides. They are, in fact, all of these. Complex inorganic color pigments are man-made materials in violet, blue, green, yellow, brown and black that are calcined at temperatures between 800 and 1,300 degrees Celsius. In the past, these pigments were used primarily to color ceramics. Today, they are one of the most important pigment classes used to color plastics and coatings. Complex inorganic color pigments are known to be heat stable, light fast, chemically resistant and weatherable.
Colors or colorants are made up of pigments and dyes. The Color Pigment Manufacturer's Association defines a pigment as “colored, black, white or fluorescent particulate organic or inorganic solids that are usually insoluble in and essentially physically and chemically unaffected by, the vehicle or substrate in which they are incorporated. They alter appearance by selective adsorption and/or scattering of light. Pigments are usually dispersed in vehicles or substrates for application, as for instance, in the manufacture of inks, paints, plastics or other polymeric materials. Pigments retain a crystal or particulate structure throughout.”
The present invention relates to the manufacture and use of titanate-based CICPs that have low metal loading (doping) levels compared with traditional CICPs. Examples of titanate-based pigments, which can be used as bases for the present invention, include the following:
C.I. Pigment Brown 24
C.I. Pigment Brown 37
C.I. Pigment Brown 40
C.I. Pigment Brown 45
C.I. Pigment Yellow 53
C.I. Pigment Yellow 161
C.I. Pigment Yellow 162
C.I. Pigment Yellow 163
C.I. Pigment Yellow 164
C.I. Pigment Yellow 189
C.I. Pigment Black 12
C.I. Pigment Black 24
The normal variety of titanate-based CICP materials in commerce today has relatively high metal doping levels (i.e., greater than about 10% by weight). As used herein, “doping level” or “loading level” refers to the amount of replacement by weight of TiO2 in the titanate lattice structures. For example, C.I. Pigment Brown 24 is made of a rutile titanium dioxide-based crystal doped with chromium (III) oxide (coloring oxide) and antimony (V) oxide (colorless charge balancing oxide). A typical composition of that homogeneous pigment in ceramic nomenclature is described in the Pigment Handbook, at page 383, as follows: Cr2O3.Sb2O5.31TiO2. In this compound, the following are the weight percents of the component elements:
Cr=3.52%
Sb=8.25%
Ti=50.29%
O=37.94%
Total doping metal content (Cr(III) and Sb(V))=3.52+8.25=11.77%
Such a formulation and other formulations with even higher metal loadings, typically between about 10 and about 20% of the total TiO2 by weight replaced by the Cr and Sb oxides, describe a common commercial C.I. Pigment Brown 24 pigment. Most conventional CICPs in today's marketplace tend to have doping levels nearer to about 20% replacement level. The reason for high levels of doping in conventional CICPs is two-fold: first, it provides a brighter color for the pigment, and second, it helps give the resulting pigment good tinting strength.
Doped rutile pigments are described in the following U.S. patents; none of them describe or include examples of doping levels less than 5%:
U.S. Pat. No. 1,945,809, Herbert, issued Feb. 6, 1934
U.S. Pat. No. 2,257,278, Schaumann, issued Sep. 30, 1941
U.S. Pat. No. 3,022,186, Hund, issued Feb. 20, 1962
U.S. Pat. No. 3,832,205, Lowery, issued Aug. 27, 1974
U.S. Pat. No. 3,956,007, Modly, issued May 11, 1976
Each of the following patents describes the use of modifiers to improve some property of the defined pigments. The '175 patent discusses improving infrared reflectivity. None of these patents suggests doping levels below 5%:
U.S. Pat. No. 4,844,741, Knittel et al, issued Jul. 4, 1989
U.S. Pat. No. 4,919,723, Wilhelm et al, issued Apr. 24, 1990
U.S. Pat. No. 5,006,175, Modly, issued Apr. 9, 1991
U.S. Pat. No. 5,192,365, Modly, issued Mar. 9, 1993
EPO Published Patent Application 1 078 956, Reisacher et al, published Feb. 28, 2001
Finally, PCT Published Patent Application WO 2011/101657, Edwards et al, published Aug. 25, 2011, suggests using rutile TiO2, at a larger size than typical, in conjunction with colored organic pigments to provide improvement in IR reflectance. Colored titanate pigments may also be combined with organic pigments in the disclosed compositions.
Solar radiation reaching the earth's surface covers a spectral range starting at about 300 nanometers (nm) and trailing off in the infrared region at about 2,500 nm. Solar radiation peaks in the visible spectral range. Still, roughly 50% of the radiation reaching the earth's surface is in the IR spectral region. This IR radiation contributes to heat build-up in exposed articles. Most of this results from radiation which is absorbed by a substrate and is converted into heat, thereby heating the entire object. An example of this would be a building, such as a storage facility, which is built from metal sheets or even cinder blocks, and which is located in a temperate (or even tropical) area. The sun beating down on this building during the late Spring and Summer months would, as a result of infrared absorption, heat the interior space of the building, thereby affecting the materials which are stored in the building.
In order to keep exposed surfaces cooler, efforts have been ongoing to increase the surfaces' infrared (IR) reflectivity. The more solar IR radiation that is reflected away from the surface, the less is absorbed and the cooler a surface will remain upon direct exposure. Achieving higher IR reflectance and cooler surfaces, can result in decreased energy consumption and lower energy costs.
The present invention provides coloring materials that are useful in boosting the solar IR reflectivity in articles in which they are used as a pigment in place of more common and conventional pigments.